This is my go-to sweet potato casserole recipe - because it's so luxurious and decadent. This is a staple for holidays, with either the nut topping or marshmallows (for those who insist). I usually don't add sugar, since roasting the potatoes gives it more than enough sweetness, especially if you roast them extra long (like 75+ minutes for large), and the topping is crazy sweet. Make sure your butter can fully incorporate into the mashed potatoes and, at the same time, the potatoes aren't so hot they cook the eggs. Both mistakes I've made. There are never leftovers of this dish.